Fritz Haber is a German chemist who uses his understanding of complex molecular reactions to develop the first chemical weapons used during World War I. Driven by a deep sense of nationalism, he views his scientific achievements as a duty to his country. He later invents a process for extracting atmospheric nitrogen, creating an artificial fertilizer that addresses global food scarcity. His intense focus on scientific advancement frequently creates friction in his personal life.

Karl Schwarzschild is a brilliant Jewish-German astronomer and former child prodigy. Despite holding a prestigious position as the director of an astrophysical observatory, he volunteers to fight for Germany in World War I. Operating from the front lines, he obsesses over astronomical equations, specifically calculating how the massive density of a dying star distorts the fabric of space and time to create a singularity.

Shinichi Mochizuki is an exceptionally gifted but painfully shy Japanese mathematician based in Kyoto. As a former child prodigy who attended Princeton at sixteen, he develops a completely new branch of mathematics to solve previously unanswerable problems. He works in near-total isolation, becoming increasingly agoraphobic and refusing to explain his theories to the broader academic community.

Alexander Grothendieck is a renowned French mathematician dedicated to uncovering the absolute foundations of mathematics. Raised in internment camps due to his parents' radical politics, he carries an intense, single-minded focus into his adulthood. He develops highly abstract geometric concepts but eventually grows fearful of the potential real-world applications of his intellect, pushing him toward asceticism.

Erwin Schrödinger is an Austrian physicist who studies the behavior of subatomic particles. Operating with limited financial means following World War I, he travels between academic posts while immersing himself in Hindu philosophy. He works in manic, highly concentrated bursts, often channeling his intense erotic fixations and vivid dreams into his mathematical breakthroughs.

Karl Heisenberg is a German theoretical physicist determined to prove that quantum particles cannot be traditionally visualized. Prone to severe allergies and intense fevers, he retreats to isolated locations to develop complex numerical matrices. He experiences profound, mystical hallucinations during his illnesses, which heavily inform his groundbreaking uncertainty principle.

Prince Louis-Victor Pierre Raymond, 7th Duc De Broglie, is an eccentric French theoretical physicist. Raised in a sheltered royal environment, he discovers a passion for science through his older brother. He isolates himself within his palace to formulate the theory that all matter exists simultaneously as both a particle and a wave.

Albert Einstein is a prominent theoretical physicist who holds immense authority in the scientific community. He firmly believes in an orderly, measurable universe and actively resists the chaotic implications of quantum mechanics. He reviews the emerging theories of his younger peers, acting as both a validator and a fierce critic of their findings.

Miss Herwig is the 16-year-old daughter of a Swiss sanatorium director. Having suffered from tuberculosis since early childhood, she possesses a serene, quasi-mystical presence that fascinates the other residents. She is highly intelligent, reading extensively and discussing complex theoretical and philosophical concepts with her tutors.

The Narrator is an unnamed middle-aged man living in a small town in southern Chile. He observes his quiet surroundings closely, paying special attention to his slow-growing garden and the remaining patches of old-growth forest. He holds a cautious curiosity about the history of his town and the eccentricities of his neighbors.

The Night Gardener is an unnamed former mathematician who has retired to rural Chile. He chooses to garden at night to avoid disturbing his plants while they are asleep. Having abandoned his academic career after studying advanced mathematical theories, he harbors a profound wariness regarding the limits of human comprehension.

Niels Bohr is a highly respected Danish theoretical physicist. He guides younger scientists through the complexities of quantum mechanics, advocating for an interpretive, almost poetic approach to physics. He actively moderates and contributes to the fierce academic debates regarding the true nature of subatomic particles.

Haber's Wife is married to the chemist Fritz Haber. She actively questions the morality of his work, specifically accusing him of perverting science by developing tools for mass casualties.

Else Rosenbach is the wife of astronomer Karl Schwarzschild. She remains at home while he serves in the German military, receiving letters in which he details the dark thoughts brought on by his calculations.

Richard Courant is a mathematician who encounters Karl Schwarzschild during his military service. He listens to the astronomer's complex theories regarding the behavior of collapsing stars.

Luc Illusie is a friend and associate of the reclusive mathematician Alexander Grothendieck. He acts as a point of contact for Grothendieck's demands to suppress his own scientific findings.

Leila Schneps is an American mathematician who tracks down the reclusive Alexander Grothendieck. She attempts to understand the reasons behind his complete withdrawal from the scientific community.

Princess Pauline is the sister of theoretical physicist De Broglie. She acts as a protective figure during his cloistered, aristocratic childhood.

Maurice De Broglie is an experimental physicist and the older brother of De Broglie. He introduces his younger sibling to the world of science, sparking a lifelong obsession with physics.

Jean-Baptiste Vasek is a painter and collector who gathers artwork created by patients of psychiatric institutions. His radical artistic theories heavily impact his close friend, the physicist De Broglie.

Annemarie Bertel is married to Erwin Schrödinger. She gives up a reliable income to travel with him to various poorly paid university positions, a situation that strains their marriage alongside mutual infidelities.

Peter Debye is a Dutch physicist who works in the same academic circles as Erwin Schrödinger. His relationship with Schrödinger's wife creates significant personal tension between the two scientists.

Dr. Otto Herwig is the director of a Swiss sanatorium where Erwin Schrödinger goes to recover from tuberculosis. He manages the care of the residents while also tending to his chronically ill daughter.

The Narrator's Daughter is a seven-year-old girl who explores the local environment with her father. She displays a natural empathy and concern for the animals in her village.